Note: Descriptions are shown in the official language in which they were submitted.
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DIGITISED HANDWRITTEN SIGNATURE AUTHENTICATION
1. Field of the invention
The invention relates to the field of authentication. More particularly, the
invention relates to the field of the authentication of handwritten
signatures.
2. Prior art
In certain sales deeds, contractual documents or subscription documents, the
undertaking party or subscriber is required to affix a handwritten signature.
To facilitate
the management of these documents, it is increasingly common to directly or
subsequently dematerialize (or virtualize) the documents as well as the
signature,
through the use of biometric or non-biometric data so as to keep only a
digital carrier.
Thus, from a legal and often psychological viewpoint, it is always necessary
to
have available a handwritten signature on a certain number of documents. There
is
therefore a need to propose a solution that enables compliance with legal
requirements
and reassures users wishing to see the appearance of a handwritten signature
while at
the same time ensuring that this signature complies with the provisions of
1999/93/EC
directive.
There are known methods and devices in the prior art that are used to enter
the
signature of an individual on to an information-processing carrier. Such
devices are for
example used by postal employees or by transporters to validate the reception,
by an
addressee, of a package or an envelope that is to be delivered by hand. The
use of such
signature devices replaces paper delivery receipts by electronic delivery
receipts. Such
electronic receipts simplify the management of acknowledgements of receipt for
organizations that use such methods. By contrast, as far as security is
concerned, the
existing devices do not perform well. These devices indeed are not made to
take account
of the legal requirements of signature authentication. On the contrary, the
only function
of existing devices is to take a signature and digitize it. Since the goal of
these devices is to
replace a paper signature by a digitized signature, the securing of these
signatures is only
rarely taken into account.
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Conversely, for the securing of electronic exchanges (such as for example
exchanges between a customer and a server), there are numerous mechanisms that
ensure that the information exchanged is confidential. These mechanisms are
implemented by means of asymmetrical keys or shared keys. Using these keys,
the
information is exchanged in encrypted form. Naturally, there are numerous
variations
and numerous methods to make sure that only the holder of a key or a pair of
keys is
capable of encrypting or decrypting a piece of information. These mechanisms
make it
possible especially to implement a signature called a "digital" signature
(legally called an
electronic signature) on documents. As a rule, a digital signature ensures the
integrity of
an electronic document and authenticates its author. A digital signature has
characteristics that enable the reader of a document to identify the person or
organization who has placed his signature and who ensures that the document
has not
been altered between the time when the author has signed it and the time when
the
reader consults it. The following are the characteristics to be brought
together so that a
digital signature may comply with expectations: the authenticity of the
identity of signing
party, the non-falsifiable character of the signature, the impossibility of
using the
signature for another document, the inability of the signed document to be
altered and
the irrevocability of the signature.
Now, given the state of the prior art, these characteristics are not often
brought
together in present-day devices for entering handwritten signatures. Thus, few
existing
devices enable an entry of handwritten signatures meeting the above
characteristics.
Some existing systems claim to be capable of providing a digitized hardware
signature
that is compliant with the European Parliament directive and the directive of
the
European Council dated 13 December 1999 (1999/93/EC). This is for the case for
example
with the WacomTM firm. However, existing systems, including those by WacomTM,
require
the use of a complementary external device (called a signature pad). Besides,
as
explained by WacomTM, communications with the WacomTM device can be controlled
by
means of a framework which is known to all and which makes it possible at the
very least
to develop a malicious software program to access the device. There is
therefore a
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security flaw in current systems. In addition, current systems offer "plain
text" or "visible"
access to the biometric data produced (these are the customers' signatures).
This is
contrary to the provisions of the European directive 95/46/CE, which
stipulates that such
biometric data should not be subject to uncontrolled dissemination
3. Summary of the invention
The invention does not have these problems of the prior art. Indeed, the
invention
makes it possible to both provide a digitized handwritten signature while at
the same
time providing the properties needed for its validation according to legal
requirements.
More particular, the invention takes the form of a method for creating a
digitized
signature. According to the invention, such a method comprises:
a step for entering a signature delivering a digitized signature;
- a step for obtaining at least one piece of data pertaining to a context
associated
with said digitized signature;
- a step for combining said digitized signature and said at least one piece
of context
data delivering a contextualized signature.
Thus, the invention makes it possible to combine, in only one signature,
elements
to clearly identify the object of this signature. The object of the signature
is therefore
linked unalterably to the signature itself. Besides, since the image can be
printed, the
invention also makes possible to have physical proof of the signature of the
deed in
addition to digital proof.
According to the invention, the above-mentioned method is implemented within a
secured enclosure. Such a secured enclosure can for example take the form of a
secured
terminal, such as a payment terminal which comprises a device or a mechanism
for
digitizing handwritten signatures.
According to one particular characteristic, said step for obtaining at least
one
piece of data relating to a context comprises at least one step for obtaining
a random
piece of data.
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Since the random piece of data is obtained at the time when the context data
is
obtained, it is also related to the deed. This means that an attacker wishing
to usurp the
signature must also retrieve this piece of random data, which is a very
complicated task.
According to one particular characteristic, said step for obtaining said piece
of
random data comprises at least one step for computing a piece of data
representing a
random image background.
According to one particular characteristic, said step for computing said piece
of
data representing a random image background comprises a step for applying a
random
noise to an original image.
According to one particular embodiment, said step for obtaining a signature
furthermore comprises a step for obtaining at least one piece of biometric
data of said
user.
Thus, this piece of biometric data can be used in the framework of the
creation of
context. The step for obtaining the signature also comprises a step for
obtaining a
digitized image and other parameters such as for example the method used to
capture
the signature.
According to one particular embodiment, said method furthermore comprises:
a step for computing at least one piece of concealed data by means of said at
least
one piece of data pertaining to a context and said at least one digitized
signature;
a step for inserting said at least one piece of concealed data into said
contextualized signature.
According to one particular embodiment, the piece of biometric data previously
obtained can be used to compute the piece of concealed data, thus making it
almost
impossible to falsify the signature.
According to one particular embodiment, said step for inserting said at least
one
piece of concealed data within said contextualized signature comprises a step
for
computing a digital watermark from said at least one piece of concealed data
and said
step for inserting said at least one piece of concealed data consists of the
application,
within said contextualized signature, of said digital watermark.
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According to one particular embodiment, said step for inserting within said
contextualized signature consists in inserting said at least one piece of
concealed data
within metadata of said contextualized signature.
The invention also relates to a device for creating a contextualized digital
5 signature representing a signature made by a user.
According to the invention, such a device comprises:
means for obtaining at least one piece of data relating to a context;
means for obtaining a signature delivering a digitized signature;
means for combining said digitized signature and said at least one piece of
context
data delivering a contextualized signature.
According to one preferred implementation, the different steps of the methods
according to the invention are implemented by one or more software programs or
computer programs comprising software instructions to be executed by a data
processor
of a relay module according to the invention and designed to control the
execution of the
different steps of the methods.
Consequently, the invention also pertains to a program capable of being
executed
by a computer or by a data processor, this program comprising instructions to
control the
execution of the steps of a method as mentioned here above.
This program can use any programming language whatsoever and can take the
form of source code, object code or a code that is an intermediate code
between source
code and object code such as in a partially compiled form or in any other
desirable form
whatsoever.
The invention is also aimed at providing an information carrier readable by a
data
processor, and comprising instructions for a program as mentioned here above.
The information carrier can be any entity or device whatsoever capable of
storing the
program. For example, the medium can comprise a storage means such as a ROM,
for example a
CD ROM or a microelectronic circuit ROM or again a magnetic recording means
such as floppy disk
or a hard disk drive.
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Besides, the information carrier can be a transmissible carrier such as an
electrical or
optical signal, which can be conveyed via an electrical or optical cable, by
radio or by other
means. The program according to the invention can especially be uploaded to an
Internet type
network.
As an alternative, the information carrier can be an integrated circuit into
which the
program is incorporated, the circuit being adapted to executing or to being
used in the execution
of the method in question.
According to one embodiment, the invention is implemented by means of software
and/or hardware components. In this respect, the term "module" in this
document can
correspond equally well to a software component as to a hardware component or
to a set of
hardware or software components.
A software component corresponds to one or more computer programs or several
sub-
programs of a program or more generally to any element of a program or a
software package
capable of implementing a function or a set of functions, according to what is
described here
below for the module concerned. Such a software component is executed by a
data processor of
a physical entity (terminal, server, gateway, router, etc) and is capable of
accessing hardware
resources of this physical entity (memories, recording media, communications
buses,
input/output electronic boards, user interfaces, etc).
In the same way, a hardware component corresponds to any element of a hardware
assembly capable of implementing a function or a set of functions according to
what is described
here below for the module concerned. It may be a programmable hardware
component or a
component with an integrated processor for the execution of software, for
example an integrated
circuit, a smartcard, a memory card, an electronic card for executing
firmware, etc.
Naturally, each component of the system described here above implements its
own
software modules
The different embodiments mentioned here above can be combined with one
another to
implement the invention.
7
4. Description of Drawings
Other features and advantages of the invention shall appear more clearly from
the
following description of a preferred embodiment, given by way of a simple,
illustratory and non-
exhaustive example, and from the appended drawings, of which:
- Figure 1 is an example of a contextualized signature as understood in the
invention;
- Figure 2 describes the method for creating a contextualized
signature as
understood in the invention;
- Figure 3 describes a method for verifying a contextualized
signature as understood
in the invention;
- Figure 4 illustrates a method for furnishing proof of signature
as understood in the
invention;
- Figure 5 illustrates a device capable of creating a
contextualized signature.
5. Description of one embodiment
5.1. Reminder of the principle of the invention
As explained here above, it has been observed that the current solutions are
not
capable of really ensuring the authenticity of the digitized handwritten
signatures for a
given deed and moreover do not ensure the confidentiality of the user's
personal data
(for example his biometric data). To date, the virtualization of a signature
commonly
corresponds to an image. Hence, a merchant or any other party who is ill-
intentioned can
copy this signature in order to affix it to another contract or to a
modification of the
contract or can use this signature obtained in the context of any other
operation. Besides,
in this case of the virtualization of signatures with biometric data, the
biometric signature
acquisition systems provide all the data to a third-party software program
that is
executed on a non-secured system. Thus, it is possible for virus type software
programs
to retrieve this personal information and use it for fraudulent purposes.
The invention makes it possible to settle and confirm the association of the
signatory's signature with elements identifying the contractual document
concerned
within the secured equipment inalterably so as to prevent the above-mentioned
flaws.
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In general, the invention relates to the signature in itself, the method of
its
creation and to methods used to verify the validity of these signatures. To
ensure trust
and security between the two parties, the inventors propose the use of an
apparatus
provided with a device for the digital acquisition of the signature with or
without
biometric data as well as a cryptographic enclosure enabling it to perform
algorithms
based on one or more secret and/or asymmetric keys. More particularly, the
inventors
propose the use of card payment terminals and the capture of signatures
corresponding
for example to the PCI-PTS standards. Thus, it is not necessary to have
available a third-
party apparatus to capture the signature and therefore only one apparatus with
a security
and signature-capture function is sufficient. An existing apparatus can be
used (if it has a
signature capture/recording device). This has several advantages. The first
advantage is
that of not depending on one particular hardware supplier. Payment terminals
that meet,
for example, the PCI-PTS standards are indeed available from several
manufacturers. The
proposed method is compatible with these terminals. The second advantage is
that of
having available a highly secured terminal (relative to the terminals of the
specialized
companies). Indeed, the pads of the specialized companies are adapted to
conventional
use. These pads do not have the same security measures as for example those of
PCI-PTS
payment terminals (which include ant-intrusion mechanisms, memory-erasure
mechanisms, cryptographic algorithmic keys, etc.). Thus, to date, it is
possible to have a
dialogue with an existing pad in order for example to obtain the cryptographic
keys
needed to encrypt the signature (to enable the production of false signatures
thereafter)
or to obtain an original digitization of an existing signature.
However, the use for example of a PCI-PTS terminal guarantees that this type
of
problem cannot arise. Thus, according to the invention, when requesting a
signature, the
apparatus (for example the PCI-PTS terminal) receives data pertaining to the
deed or
document (of sale, contract or subscription). The apparatus computes a
certificate of
operation pertaining to this data and then acquires the signature. Naturally,
the use of a
PCI-PTS terminal can be replaced by that of another type of terminal provided
that this
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terminal firstly secures the data entered and secondly comprises means for
detecting
intrusion and/or fraud.
To enable the certification of the signature at the point of sales, contract
or
subscription, the terminal provides a contextual signature of the deed or
document (of
purchase, contract or subscription) in the form of a contextualized image
(this is a specific
image as will be shown here below). The enormous advantage is that this image
can be
printed and can serve as a payment ticket. In certain embodiments, this
payment ticket
can also serve as subsequent proof. This signature is described with reference
to figure 1.
The general certificate 10 (or contextualized certificate or contextualized
image)
comprises a random element 11 (for example a random background (for example of
the
white noise type commonly called snow)) on which at least two other images are
superimposed. The first image 12 comprises data on the document (this is a
context or
contextual data) combined in one certificate called an operation certificate
computed by
the equipment and incontestably identifying this document. This first image 12
can also
contain all the data needed to verify this certificate of operation and, if
necessary, legal
information on use pertaining to the contextualized signature.
The second image 13 comprises a graphic rendering of the signature.
Finally, all or part of the data received or acquired by the apparatus at the
time of
the deed as well as the certificate of operation (the data serving to identify
the deed such
as identifiers, amounts, dates and times, etc.), the data serving for its
control and
optionally the legal information on terms of use can be encrypted or concealed
or
recorded in the contextualized signature. The biometric parameters of the
signature
collected can form part of this data thus integrated or concealed. This data
is invisible
(and therefore not shown in figure 1). It can take the form of either a
digital watermark or
metadata included in the image.
The final contextualized image provided by the apparatus thus constitutes an
electronic signature as understood in the directive of the European Parliament
and of the
European Council dated 13 December 1999 (1999/13/EC).
10
Indeed, the identity of the provider of the deed, also called the contractual
partner, is guaranteed by the use of a terminal and the identity of the
subscriber, also
called the signatory, is guaranteed by his signature, of which he is the only
person to hold
the means of producing this signature. The integrity of the contextualized
signature is
guaranteed by the certificate of operation and the data of the handwritten
signature
present and recorded in the image. In addition, for the use of biometric data,
the
protection of this biometric data (which is personal data) is complied with by
encryption
in accordance with the European directive 95/46/EC.
Consequently, the invention does not require an uncontrolled third-party
system
(i.e. a third-party system which is not a trusted party) to produce a
contextualized
signature which has the value of an electronic signature as understood in the
directive
99/13/EC. By contrast, according to the invention, as explained here below,
the presence
of a trusted third party can be useful to establish proof of the signature in
the event of
dispute.
This image is transmitted to a requesting device or third party, if necessary,
with a
view to printing, saving or archival storage.
5.2. Creation of the contextualized signature
Referring to figure 2, we present the different steps that lead to the
creation of a
contextualized signature as understood in the invention. It may be recalled
that a
contextualized signature is a signature linked to a given deed or document,
whether it is a
deed or document of purchase, sale or subscription. More generally, a
contextualized
signature is a signature attached to a contract or to a commitment.
According to the invention, in this embodiment, the creation of a
contextualized
signature comprises a step 200 for obtaining a random image 20 (in one
particular
embodiment, the random image is a white background image to which a random
monochrome noise is applied, itself defined by a random factor in the form of
an
alphanumerical sequence of characters). Once this random image has been
obtained, the
method comprises a step 201 for obtaining a digitized signature 21. The step
21 for
obtaining comprises either the entry of the signature by a user on the
terminal and/or the
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obtaining of a signature file (SIG file containing biometric data). The step
for obtaining a
signature also comprises a step for obtaining a digitized image and/or other
parameters
such as for example the method used to carry out a capture (2D, 3D, sampling
rate, etc.).
The method also comprises a step 202 for obtaining transaction data 22 (or
transactional
data). This transactional data corresponds to the context for which the
signature is made.
Should it be a purchase, this transactional data comprises for example the
vendor's
identifier, the date and time, the amount of the transaction, the customer's
identifier
(signatory), the type of signature made to validate the transaction.
This last-mentioned characteristic is directly related to context. Indeed,
depending
on the terminals, it is possible to pick up a signature according to various
methods.
Certain captures can be made only in two dimensions. Other signatures can be
captured
in three dimensions. Since the tradesman (or holder of the terminal) knows the
type of
signature that is being picked up by the terminal, this type of signature,
according to the
invention, is integrated into the transactional data. This makes it possible
to link the
signature even more strongly to a particular context.
The following step consists in merging 203 the random image 20, the signature
21
and a graphic representation 23 of the transactional data 22 in one and the
same
combined image 24. This combined image 24, according to a first embodiment,
forms the
contextualized signature as understood in the invention. According to one
particular
characteristic, the method furthermore comprises a step 204 for building
concealed data
and a step 205 for the insertion, in the form of a digital watermark 26 (or
metadata),
of concealed data in the combined image 24 to form a watermarked image 27. In
this
second embodiment, the watermarked image 27 forms the contextualized
signature.
According to one particular characteristic, the concealed data 25 comprises
25 biometric data and/or transactional data and/or image building data (for
example the
digital string representing the random element used). The biometric data are
pieces of
data representing the captured signature 21. Depending on the method used to
capture
the data (for example 3D signature capture or 3D capture with or without data
on
pressure), the biometric data comprise information different in various
degrees. Thus,
12
according to the invention, the pieces of biometric data are integrated into
the
contextualized signature. However, to comply with the legislation in force
(the directive
95/46/EC especially), this biometric data is not only concealed but, in
addition, is not
integrated "in plain" or visibly into the signature. On the contrary, the
biometric data is
encrypted prior to its integration in concealed form in the contextualized
signature. More
specifically, the concealed data is preliminarily encrypted by using the
cryptographic
material of the terminal (for example the payment terminal when this type of
terminal is
used). Since the terminal is protected and secured, it is thus ensured that
only the holder
of the cryptographic material of the terminal (the holder of the cryptographic
equipment
is for example the manufacturer of the terminal) can decrypt this encrypted
data and
meet the requirements of authentication which can arise at the end of the
signing
process.
5.3. Determining of proof of the deed
After the contextualized signature has been created, two situations can arise.
The
first situation is the request, transmitted by a requesting third-party
establishment,
tending to obtain proof of signature by the contracting party (this for
example can be
proof of payment required by a bank). According to the invention, this request
is met by
the transmission of an assertion of validation of the contextualized
signature. The method
of issuing this assertion is described with reference to figure 3.
Two possible instances can occur in this first situation. In the first
instance 301, the
contractual partner 30 (for example the merchant), directly uses the secured
image file
(this is the contextualized signature 24, 27) in his possession. In this case,
he can transmit
it to the requesting party 31 (for example a financial institution that wishes
to obtain
proof of purchase or of the deed). In the second example, if the financial
establishment
31 wishes to have proof of authenticity of this contextualized signature 27,
the
contractual partner 30 who has this contextualized signature 27 available,
transmits it
302 to a trusted or trustworthy third party 32 responsible for authenticating
it. This
trusted third party 32 will, on the basis of this contextualized signature 27
alone, carry out
the operations needed to recreate the signature. In this embodiment, the
trusted third
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party 32 is deemed to be in possession of the cryptographic equipment needed
for
decrypting the concealed data 25 of the contextualized signature 27 (for
example the
trusted third party possesses the private key used to encrypt the concealed
data 25). This
trusted third party 32 can be the builder of the terminal that has been used
to build the
contextualized signature.
In this embodiment of the invention, the following step is a step 303 for
extracting
concealed data 25 followed by a step 304 for decrypting the concealed data 25
delivering
biometric data and contextual data (DB-DC). The requesting party 31 transmits
305, for
his part, the transactional data (DT) in his possession. At least some of the
data (DB-DC) is
then compared 306 with at least some of the transactional data (DT) and an
assertion A is
transmitted 307 when the data are in agreement. As an alternative, the trusted
third
party 32 can receive the transactional data DT from the contractual partner 31
(if he
possesses it). As an alternative, the trusted third party 32 can already have
a copy of the
transactional data DT. The invention also pertains to the computer programs
and the
devices used to implement the method that has just been described.
5.4. Checking the validity of the contextualized signature
The second situation is that in which it is necessary to prove that a
signature has
not been artificially forged, outside the method for creating the
contextualized signature
and/or that the transactional data has not been modified.
The method of verification is described with reference to figure 4.
This method comprises:
- a step (400) for receiving transactional data (41) from a
custodian or depository
(40), by a trusted third party (TC), this transactional data (41) being taken
to be
the source of the contextualized signature (42) the authenticity of which is
to be
verified (the custodian can be the merchant, the entity having the quality of
a
contractual partner or a trusted third party with whom the transactional data
is
preserved);
- a step (401) for receiving the contextualized signature to be
verified (42) from a
custodian (43. It may be the same custodian but this is not obligatory;
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a step (402) for searching, within the contextualized signature to be verified
(42)
for a digital watermark or for metadata (44) delivering a piece of data on the
presence of digital watermarking or metadata; and
- when said piece of data on presence of a digital watermark is positive, a
step (403) for obtaining concealed data (45);
- when said piece of data on the presence of a digital watermarking is
negative, a step (R) for rejecting said contextualized signature;
a step (404) for checking the concealed data (45); and when certain pieces of
said
concealed data correspond to at least certain pieces of said corresponding
transactional data (41),
- a step 405 for computing a signature, comprising a step for decrypting
biometric data, a step for building a signature (SG) from the biometric data
included in the decrypted concealed data;
a step 406 for building a contextualized reference signature (SCR) from said
preceding data. The building comprises, if necessary, the implementing of
the random factor included in the concealed data;
a step for comparing said reference signature SCR and said contextualized
signature 42;
when the two signatures are different, a step (R) for rejecting the
contextualized signature;
when the two signatures are identical, a step (408) for checking the
authenticity of the biometric data (this verification is done by other means
not described herein) and when the biometric data is the right data, a step
(409) for transmitting a piece of information on authenticity of the
signature.
Thus, as shall be seen clearly from the reading the above, the contextualized
signature comprises both a handwritten signature that is visible and directly
identifiable
by a user and the data needed to rebuild this signature for the subsequent
checking of its
own authenticity. A remote analogy can be made with a living cell which
comprises both
15
its own characteristics and means to duplicate itself to obtain an identical
cell. The
invention also pertains to computer programs and devices enabling the method
that has
just been described to be implemented.
5.5. Content of the concealed data
In one purely illustratory embodiment, the concealed data comprise the
following
data recordings:
- at least one piece of data for identifying the signatory;
- at least one piece of data for identifying the contractual
partner (for example the
merchant, the entity issuing the contract or the deed);
- at least one piece of data for dating the signature;
- at least one piece of data for identifying the signature;
- at least one piece of data for identifying a trusted third party;
- a piece of data for identifying an encryption key;
- a piece of data for identifying a key version;
- a piece of data for identification of a key derivation;
- a computerization of a random element (this is for example an
alphanumerical
sequence of predetermined length);
- encrypted biometric data.
It is possible to complement or replace this concealed data by other data
which
can have relevance depending on a given context.
5.6. Device for creating a contextualized signature
Referring to figure 5, we describe a device 50 for creating a contextualized
signature as understood in the invention. Such a device comprises signature-
capturing
means 51. Such means are for example a touch screen capable of recording a
signature. It
may also be a signature pad dissociated from the display of the entered
signature.
Be that as it may, this device comprises:
- means 52 for obtaining at least one piece of data pertaining to a
context. These
means can take the form of a software or hardware module or again a network
module for the reception of information from another device. It can also be
all
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these means together to enable the data coming from several sources to be
combined.
means 51 for entering a signature delivering a digitized signature, namely
means
incorporating means for obtaining biometric data (i.e. from the signature
performed; the pieces of biometric data are computed by these signature entry
means) or these means are solely responsible for the capture of data which
must
then be processed and analyzed by another module 53 to produce the biometric
data.
means 54 for combining said digitized signature and said at least one piece of
contextual data delivering a contextualized signature. These means for
combining,
which are integrated into the device, comprise for example secured memories
comprising encryption keys, means for generating random values when necessary,
means of encryption, means for formatting data, etc. These means can be
software modules implemented by a processor, hardware modules, for example
programmable hardware modules, or again a specialized processor performing all
these tasks.
Besides, the device furthermore comprises interfaces (55, 56), for example
network interfaces R enabling the transmission and reception of computer data
to other
devices such as servers to enable firstly the reception of requests for
furnishing
contextualized signatures, the transmission of such signatures of context
alone, etc.
